1. Field of the Invention
The present invention relates to a rotary table apparatus and an electric discharge machine including the rotary table apparatus.
2. Description of the Related Art
FIG. 6 schematically illustrates a cross section of a rotary table apparatus for, for example, an electric discharge machine. As illustrated in FIG. 6, a casing 1 of a rotary table (rotary table apparatus) 24 encloses a power unit 2 and a speed reducer 3. The speed reducer 3 reduces the rotation speed of the power unit 2. A bearing support 7 is disposed in a front end of the casing 1 and supports a bearing 4. A shaft 5 is fixed to one end of the bearing 4 and a faceplate 6 is fixed to the other end of the bearing 4 in such a manner that the shaft 5 and the faceplate 6 are freely rotatable in synchronization with rotation of the speed reducer 3. A seal mechanism 8 is disposed near the bearing support 7 and includes a sealer 9. The sealer 9 is in contact with an outer peripheral surface of the faceplate 6 so as to prevent working fluid from entering the casing 1 through a clearance 11 between the seal mechanism 8 and the faceplate 6.
During machining of a workpiece with an electric discharge machine, machining waste called sludge is generated and suspended in working fluid in a work tank. As indicated by a flow 18 of working fluid containing sludge, when working fluid containing sludge enters the clearance 11, sludge is attached between the sealer 9 and the faceplate 6. Accordingly, abrasion of the sealer 9 is induced in an early stage. Typical seal mechanisms of rotary tables proposed to date include a mechanism employing an air-seal structure and a mechanism employing a labyrinth structure (see Japanese Unexamined Patent Application Publications Nos. 2011-104725 and 2008-272853).
In application, a rotary table apparatus for an electric discharge machine is placed on a work table disposed in a work tank filled with working fluid, and a workpiece is fixed on a face plate. A seal mechanism is provided in a clearance between a rotary table casing and the face plate so as to prevent working fluid in the work tank from entering a rotary table (see Japanese Unexamined Patent Application Publication No. 2005-118915). However, sludge (fine metal powder) generated during machining flows into the seal mechanism, resulting in a significant degradation of sealing performance.